Around each healthy tooth in the mouth of a human is a narrow groove termed a sulcus, which separates the tooth from the surrounding gingival tissue at the surface of the tissue. Certain dental procedures, such as those to create an impression of the tooth and those to create a prosthetic for the tooth, require that the gingival tissue be retracted from the tooth in the area of the sulcus. While the prior art teaches several means of accomplishing this retraction, none is optimal.
One commonly employed conventional method is through the use of retraction cord. Simply described, retraction cord is length of cord that is wrapped around the base of the tooth several times and then manually forced into the sulcus by a dental practitioner. The manual force will cause the gingival tissue to separate from the tooth and the presence of the cord will prevent the tissue from returning to its original state. Unfortunately, the use of retraction cord has several drawbacks. First, the cord is typically supplied by manufacturers wound on a spool, packed into a container. To use the cord, the dental practitioner must estimate the amount required for the particular application. Since the cord must be wrapped around to tooth while the ends are held in one hand by the practitioner, a significant amount of cord is wasted in the process. Second, it is very difficult to force and maintain the cord within the entire sulcus (around the entire circumference of the tooth) at the same time. It is very common for the force required to insert the cord into one area of the sulcus to cause cord already inserted to other areas of the sulcus to exit the sulcus. This requires the practitioner to repack those areas causing tearing and abrasion of the inner lining of the sulcus, leading to bleeding and/or exuding of crevicular fluid, which may cause contamination and/or inaccuracies in the dental procedures to be performed. Third, inherent in the process is that the cord does not conform well to the various depths and widths of the sulcus nor the irregularities of any prepared tooth margins. Finally, the entire process is relatively time consuming. Removal of said cord with a dental instrument is a delicate procedure often leading to trauma and bleeding of gingival tissue.
Another type of retraction cord is made of strands of a fiber such as cotton stiffened with a stiffener strand such as for example a copper wire threaded through the core of the cord. The stiffener is made of material that provides the cord with deformability. Positioning of this type of the cord over the whole periphery of the tooth is delicate. In addition, because of the stiffener strand, this process is relatively painful and generally requires a local anesthesia. Moreover as one end of this stiffened strand is packed into the sulcus, the other end tends to become displaced out of the sulcus. A frequent lesion is observed of the epithelial attachment as well as hemorrhages or oozing upon withdrawal of the cord. In addition, this type of cord suffers from some of the other above-noted drawbacks associated with retraction cords.
A second commonly employed method is through the use of an injectable paste. In this method a relatively large needle is placed in the sulcus and is used to inject a biocompatible paste therein under relatively high pressures (between 13,000 and 30,000 Pascals). This method too has several disadvantages. Typically, either the needle itself or the paste injected under high pressure or both cause trauma to the gingival tissue. Moreover, the paste is stiff and does not adhere well to moist tissues and typically is displaced out of the sulcus. This paste must often be packed down into the sulcus with a piece of cotton or a dental instrument. Because of the high pressures involved, the paste injection device (commonly termed a “gun”) is complicated, expensive and suffers frequent breakdowns (as does the actual paste container). Furthermore the paste must be washed off with a water spray and then dried with compressed air before the impression can be taken. This is an additional step and this water and then air spray will often lead to bleeding within the sulcus.
A third method is the use of a ring of material or a metal collar which is placed into the sulcus with an instrument and which is used to retract the gingiva away from the tooth. These rings have the same problem as the strands and cords in that an instrument is needed to pack the ring into the sulcus causing discomfort, bleeding. They must be retrieved and or removed with a dental instrument prior to the taking of an impression, which also causes discomfort, bleeding and trauma.
A third conventional method is the use of a pressure cap. A pressure cap is a cap made of a spongy material that is fitted around the tooth and causes retraction of the gingival tissue through the application of pressure. The difficulty here is that the shape of the cap is even and constant while that of the sulcus (depth and width) is not. Therefore this method is imprecise and does not ensure accurate nor sufficient retraction. For these reasons, it is presently only used to ensure haemostatis after a procedure of gingival eviction (described below).
An additional convention method is termed gingival eviction. In this method the gingival tissue is retracted by electric bistoury, laser, or by a diamond charged drill (“diamond curretage”). None of these procedures, however, is not without its drawbacks. Electric bistoury and laser generally mutilate the gingival tissue and are therefore quite painful and require local anesthesia. Similarly diamond curretage is also quite painful and causes prolific bleeding. Each of these procedures is traumatic and creates gingival shrinkage and recessions leading to undesirable unprotected root coverage.
There is therefore a need in the art for an improved apparatus for, and method of, retracting gingival tissue from a tooth, which are preferably more efficient and less traumatic than conventional methods.